Drive control system for powered wheelchair

ABSTRACT

A powered wheelchair is operated by sensor-based control pads that include force transducers to produce a variable output signal that is proportional to a varying force applied. The control pad provides an analog-type output that provides a variable speed signal to a controller to operate the wheelchair at a variable speed in both forward/reverse directions and in right or left turning directions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional patent application of U.S. patentapplication Ser. No. 15/514,720, filed Mar. 27, 2017. U.S. patentapplication Ser. No. 15/514,720, filed Mar. 27, 2017, is the U.S.National Stage patent application of PCT/US2015/52470, filed Sep. 25,2015. PCT/US2015/52470 claims the benefit of U.S. ProvisionalApplication No. 62/056,246, filed Sep. 26, 2014, and U.S. ProvisionalApplication No. 62/055,100, filed Sep. 25, 2014. The disclosures ofthese applications are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

This invention relates in general to power wheelchairs and, inparticular, to control devices for operating a power wheelchair.

Power wheelchairs provide improved mobility to persons having limitedambulatory capacity. In order for the power wheelchair to be effectivein improving one's mobility independence, a user must be able to operateand control the speed and direction of the wheelchair. Depending on thelevel of disability, dexterity, and cognitive capability, various inputdevices are used to provide desired commands to the controller foroperation of the unit. The joystick input device is a general inputdevice having a control stalk that translate forward and backwardmovement of the stalk to forward and backward movement of the chair andsideway motion to turn commands. This input device is common and relieson a higher level of dexterity and ability in order for the user toproperly control the wheelchair.

For users having severely limited or nonexistent use of their hands, asip-and-puff input device permits control of the wheelchair by pressureor vacuum signals activated by a user's mouth. The sip-and-puff inputdevices generally provide a step function type of input that lacks theanalog-type control capability of the joystick. Thus, control of thewheelchair may be less fluid and comfortable for the user. This is aparticularly problematic condition since these users have a very limitedrange of motion and no physical reaction capability to jerky or abruptcontrol movements. Thus, it would be desirable to provide an inputdevice that can provide an analog-type of input which varies inintensity of control; i.e., increases or decreases in speed and/ordirection; similar to a joystick input device.

SUMMARY OF THE INVENTION

This invention relates to an analog-type input device for control of apower wheelchair that provides a continuously proportional input signalin response to contact and pressure commands from areas of a user'shead. Alternatively, other areas or appendages, such as a user's neckand chin, the palm and backside of a user's hand, and a user's arm mayactuate the sensor arrays.

This invention relates to a powered wheelchair drive control systemhaving a head array and a controller. The head array has at least onepad having at least one of a force sensor proportionally responsive toan applied force from a user's head against the at least one pad and acapacitive sensor responsive to the proximity of a user's head relativeto the at least one pad. The controller operates a wheelchair drivemotor in response to signals generated by the at least one force sensorand capacitive sensor activated by a user's head.

In another aspect of the invention, the capacitive sensor of the poweredwheelchair drive control system provides an active state signal inresponse to the presence of the user's head and an off state signal inthe absence of the user's head. The controller is programmed to operatea wheelchair drive motor at a predetermined speed level in response tothe capacitive sensor generating an active state signal.

In yet another aspect of the invention, the head array includes left,right and center pads, where each pad includes a force sensor inaddition to capacitive sensors. The controller is programmed to beresponsive to the capacitive sensor in the center pad to activate apredetermined speed range in one of a forward and a reverse direction.The force sensor generates a proportional speed signal in the one of theforward and reverse directions within the predetermined speed range.

In yet another aspect of the invention, the controller responds to thecapacitive sensor in the left pad to activate a left turn direction anda predetermined left rate of turn and responds to the capacitive sensorin the right pad to activate a right turn direction and predeterminedright rate of turn. The controller may be programmed with thepredetermined forward speed range and the predetermined left rate ofturn and the predetermined right rate of turn and further programmed toadjust a force parameter associated with the force sensor. Thecontroller may also be programmed to capture an output value of at leastone of the left, right, and center force sensors in response to aninitial active state signal from the corresponding left, right, andcenter capacitive sensor. In certain embodiments, the controller isprogrammed to equate the output value of the force sensor to a thresholdvalue such that the controller responds to force output signals from theone of the left, right and center force sensors that is above thethreshold value.

In another aspect of the invention, the controller responds to thecapacitive sensor in the left pad to activate a left turn direction anda predetermined left rate of turn and responds to the capacitive sensorin the right pad to activate a right turn direction and predeterminedright rate of turn. The controller may also include an algorithm havinga transfer function that limits the proportional output of the forcesensor to a range between one of the predetermined forward speed range,the predetermined left rate of turn and the predetermined right rate ofturn and a corresponding maximum forward speed, maximum left rate ofturn, and a maximum right rate of turn.

Various aspects of this invention will become apparent to those skilledin the art from the following detailed description of the preferredembodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a power wheelchair in accordance withthe invention.

FIG. 2 is an exploded perspective view of an embodiment of a head arrayassembly and controller of the power wheelchair of FIG. 1.

FIG. 3 is a perspective view of another embodiment of a head arrayassembly having alternative adjustment capability.

FIG. 4 is an exploded view of the head array of FIG. 3.

FIG. 5 is a schematic illustration of the head array sensor andcontroller components in accordance with the invention.

FIG. 6 is a schematic illustration drive control system with aprogramming input device in accordance with the invention.

FIG. 7 is a flow chart illustrating initialization steps of a softwarealgorithm that controls the various embodiments of the sensor cushionpad in accordance with the invention.

FIG. 8 is a flow chart illustrating a software algorithm for anullification (zeroing) sequence of a force sensor portion of thesensing cushion pad in accordance with the invention

FIG. 9 is a graph of a transfer function of the algorithm forcontrolling the various embodiments of the sensor cushion pad inaccordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, there is illustrated in FIG. 1 a powerdriven wheelchair, shown generally at 10. The exemplary power wheelchairis illustrated as a mid-wheel drive wheelchair, however, it should beunderstood that the power driven wheelchair 10 may be of a front wheeldrive configuration, rear wheel drive configuration, or other suitabledrive configuration. The wheelchair 10 includes drive wheels 12 andstabilizing caster wheels 14 as are well known in the art. Thewheelchair 10 further includes a seat 16 and backrest 18. The backrest18 supports a head array assembly, shown generally at 20, as shown indetail in FIG. 2. The head array assembly 20 includes a headrestassembly, shown generally at 22, having a center pad 24, and left andright side pads 26 and 28, respectively. The left and right side pads 26and 28 are adjustably hinged from the sides of the center pad 24 andconfigured to be accessible by the user's temple region. In oneembodiment, each of the left, center, and right pads of the headrestassembly 22 include at least one sensor configured to receive an inputsignal from a user and output an operating command signal to acontroller 30. In another embodiment, the left and right pads includesensors that send operating command signals to the controller 30.

As will be explained in detail, the sensor may be configured as a forceor pressure sensor providing an output that that is proportional to andresponsive to a force applied thereto. The sensor may also be configuredas a capacitive sensor providing an output indicative of and responsiveto the proximate position of a user's body portion to the sensor. Thesensor may also be two or more sensors responsive to force and position.It should be understood that the head array is an exemplary embodiment.Other cushion structures and drive control input configurations can beused. For example, in one embodiment, the seat back and armrests can beconfigured to function in a similar manner to the center pad and sidepad operation described below in detail. Alternatively, the senorarrangement may be used in conjunction with a conventional joystick orin the form of an elbow drive device, knee drive device, and the like.In the illustrated embodiment, the headrest assembly 22 may be supportedby an angle adjustable and linearly extendable support post system 32.Alternatively, the headrest assembly 22 may be supported by any suitablemounting arrangement such as a rod extending from an upper surface ofthe backrest 18.

Referring now to FIGS. 3 and 4, there is illustrated an alternativeembodiment of a head array assembly, shown generally at 34. The headarray assembly 34, when considered as a control device, is functionallysimilar to head array assembly 20 with respect to function and sensortypes. The head array assembly 20 may have sensors in the left and rightpads 26 and 28. Thus, left and right turns of the wheelchair 10 are mayby applying greater pressure to pad situated toward the desired turndirection. Forward motion of the wheelchair 10 is obtained by pressureapplied to both left and right pads 26 and 28. The head array assembly34 includes sensors in all three pads and additional adjustmentcapability to position side pads relative to the user's head. The headarray 34 includes a center pad, shown generally at 36 and left and rightside pads 38 and 40, respectively. The center pad 36, and left and rightside pads 38 and 40 are mounted to a support frame 42 that connects to apivot mount 44. The pivot mount 44 is also shown as part of the supportpost system 32. The left and right side pads 38 and 40 are pivotallysupported by axially adjustable rods 46 that couple to the support frameby rod swivel mounts 48.

As shown in FIG. 4, the center pad 36 includes rear shell 50 configuredto contain and support a circuit board 52, at least one force sensor 54,a cushion 56, at least one capacitive sensor 58, and a covering material60. The circuit board 52 provides electrical and communicationconnectivity between the sensors 54 and 58 and the controller 30. Theforce sensor 54 is configured as a variable resistance device thatchanges resistance and provides a signal output that is in proportion,or in an inverse proportion, to the magnitude of the force applied tothe sensor 54. One example of such a force sensor is an FSR400-seriessensor produced by Interlink Electronics, though other proportionalforce sensors may be used if desired. As a user's head presses againstthe center pad 36, a force is transmitted to the force sensor 54. Anoutput signal indicative of the force and proportional to changes in theapplied force (increases or decreases in force magnitude) is generatedand sent to the controller 30. In one particular embodiment, as theforce is applied to the force sensor 54, the resistance of the sensordecreases. This force sensor output signal provides a first commandsignal, such as a speed signal, to the controller 30. In one embodiment,the force sensor 54 is a pair of force sensors 54, as shown in FIG. 5though any suitable number of sensors may be used.

The capacitive sensor 58 is positioned on one side of the cushion 56(proximate to a user's head) and the force sensor 54 is positioned onthe other side of the cushion 56. The capacitive sensor 58 provides anoutput signal indicative of the proximity of the user's head relative tothe center cushion 36. In one embodiment, the capacitive sensor 58 actsas an on/off switch device. An example of such a capacitive sensor iscapacitive sensor model no. CBN10-F46-E2, produced by Pepperl and Fuchs.In one embodiment of a control strategy used by the controller 30 and acontrol algorithm, the capacitive sensor 58 provides a signal that isused to calibrate or null output of the force sensor 54 based on theuser's head position in the head array 34, as is shown in theprogramming flow charts of FIGS. 7 and 8. In another embodiment, thecapacitive sensor 58 functions to reproduce the familiar step functionoperation of a sip-and-puff type of input device, as will be explainedbelow. The center pad 36 is covered with the covering material 60 toprovide user comfort, protect the user against skin abrasions, andprovide an aesthetic appearance.

The side pads 38 and 40 will be described in conjunction with the rightside pad 40, though the side pads are the same for each side. The sidepad 40 includes a mounting plate 62 that supports a split collar 64 toadjustably mount the side pad 40 to swivel balls at the ends of the rods46. A circuit board 66 is supported by the mounting plate 62 and mayinclude a force sensor 68. The force sensor 68 is similar in functionand operation to force sensor 54 of the center pad 36. A cushion 70,such as a foam pad, is placed against and covering the force sensor 68.A capacitive sensor 72 is supported on the opposite side of the cushion70 and the assembly is covered with a covering material 74. Anelectrical line 76 conveys the signals produced by the force sensor 68and the capacitive sensor 72 to the controller 30. The side pad 40functions in a similar manner to the center pad 36. As a user presseshis right temple, for example, against the pad the force sensor 68measures the force and send a signal to the controller that isproportional to the force applied. Side pad 38 provides a second signalindicative of a turning command, such as a left turn command. Side pad40 provides a third signal indicative of a turning command, such as aright turn command. Thus in one embodiment, as the user presses his headagainst the right side pad 40 with increasing pressure, the controller30 causes the wheelchair to turn right with an increasing turning rate.This analog-type output provides the same response in the wheelchair asmoving a joystick to increasing positions toward the right causes anincreased right-hand turning rate.

In an alternative embodiment, the center, left, and right pads 36, 38,and 40 may operate based on the capacitive sensor 58 of the center pad36 and capacitive sensors 72 in each of the left and right side pads 38and 40. In such an operating mode, the capacitive sensors 58 and 72 actas on/off switches to provide operations of turning and drivingfunctions of the wheelchair at preselected speeds, similar to the stepinputs of sip-and-puff devices. As shown in FIG. 6, a programming inputdevice 78, such as for example a pendant, computer, joystick, or dongle,may be used to program the controller 30. The pendant 78 provides theability to input discrete speed range settings 80, for example fivespeed ranges 1-5, that set operating speeds from slow (1) to full speedcapability (5) in discrete step functions of increasing speedcapability. Additionally, the pendant 78 may be able to adjust the forcedetection or response sensitivity by a force parameter 82. Thisadjustment may also be able to tune the force parameter in a temporalcondition to account for spasms that may be inadvertently inputted bythe user. When the capacitive sensor 58 detects a user, the wheelchairoperates in a forward direction at the preprogrammed speed associatedwith the center pad 36. Similarly, when the user moves his head toactivate capacitive sensor 72, the wheelchair will turn at thepreprogrammed speed associated with either the left pad 38 or right pad40.

In yet another embodiment of the drive control system, the operation ofthe force sensor is overlaid on the operation of the capacitor sensor,as will be explained in conjunction with operation of the center pad 36for forward or reverse control. In this control strategy, the capacitivesensor 58 detects the presence or absence of the user's head andfunctions as an on/off switch. The output of the capacitor sensor 58invokes the preprogrammed speed range (1 through 5) in the controller30. Detection of the user initiates forward (or backward) movement ofthe wheelchair 10 at the programmed speed range. The user then actuatesthe force sensor 54 by pressing into the center pad 36. This forcesignal actuates the controller 30 to increase the speed of thewheelchair 10 in accordance with the force level detected by the forcesensor 54. In one embodiment, the coupled operation using capacitive andforce sensor inputs varies the speed in conjunction with a transferfunction 200 represented in FIG. 9.

In this configuration, the drive control system can be customized toaccommodate users having either reasonable neck muscle usage orasymmetric coordination or muscle control. For example, where a user hasgood, symmetrical neck muscle coordination and control, the system maybe configured such that the capacitive sensor 58 initiates the lowestspeed range setting. The force sensor 54 responds to the user's pressureinput to ramps the speed up or down according to the transfer function200. The side pads 38 and 40 may be programmed to respond in the samemanner. Thus, the system operation mimics the operationalcharacteristics of a joystick input device. In situations where the userexhibits asymmetrical muscle control, for example having more ability tomove his head to the left rather than the right, the system may becustomized where the left side pad 38 is programmed with more relianceon speed control from the force sensor 54 and using a slow speed settingtriggered by the capacitive sensor 58. The right side pad 40, where theuser has less capability to actuate pressure based speed increases, maybe programmed with a higher speed range triggered by the capacitivesensor 58. The wheelchair 10 would turn right more in line with thefamiliar functions of a step input device yet still respond to whateverpressure signal the user may be able to provide.

Referring now to FIG. 5, there is illustrated schematically anembodiment of the head array assembly 34 where the center pad 36supports two force sensors 54 and two capacitive sensors 58. Thesesensors are supported, at least electrically, by the circuit board 52and may have common outputs as shown or separate outputs such that thecontroller 30 provides a blended or combined force signal and a separateblended or combined capacitive proximity signal.

Referring now to FIGS. 7 and 8, the programming flow charts illustratethe steps of initializing and adjusting the pad sensitivities of thesystem during a start up operation (FIG. 7) and system function duringthe “drive mode” operating environment (FIG. 8). As shown in FIG. 7, thestartup sequence 100 begins at step 102 when the system is initiallypowered. Preset parameters stored in the memory of the controller 30 arerecalled and the system is initialized with a zero speed and turn input.The drive mode 104 is entered. The drive mode 104 is shown in detail inFIG. 8. The drive mode 104 may be exited by a “set” step 106. The setstep 106 is entered by the operating programming pendant 78 andactivating the set button 106 a. Once activated, each of the pads andrelated sensors may be programmed and adjusted for a user's specificneeds. The sensor programming order is merely illustrative and may beconducted in any sequence desired. In a first pad programming step 108,a left pad programming button 108 a is activated permitting the abilityto adjust the capacitive and force sensor parameters, as describedabove. For example, an attendant may program the speed range activatedby the capacitive sensor 72 by stepping through entries with a speed or“crawl” button 110 a at prox. speed step 110. Then, a force parameterinput step 112 may be entered by activating a force button 112 a. In oneembodiment, the force parameter may be related to the sensitivity of theforce sensor or the resistance range associated with the force sensor.Other parameters associated with the force sensor may be varied duringthis step, if desired. In one embodiment, the inputted values may bestored by activating the set button 106 a. Similar programming may beconducted for a center pad programming step 114 and a right padprogramming step 116. Once the parameters have been saved, the drivemode 104 may be reentered.

As shown in FIG. 8, within the drive mode 104 the system performs acheck of each capacitive proximity sensor and force sensor at step 120.The drive mode 104 portion of the algorithm then check if one of thecapacitive sensors has been activated at step 122. In one embodiment,the algorithm may iterate between steps 120 and 122 until all sensorshave been checked. When a capacitive sensors is determined to be active,a null point or threshold value for the force sensor is created based onthe force sensor reading at that instant. The force sensor output isscaled from the null setting such that the initially read force becomeszero and additional pressure applied initiates movement from this newzero point at step 126. The algorithm then iterates between verifyingthat the capacitive sensor is still active at step 128 and, if so,maintains the null values and provides the force sensor outputs inproportion to the pressure input from the user. If the capacitive sensoroutput is not detected, the step 128 proceeds back to step 120 andbegins the sensor check again.

Referring now to FIG. 9, the transfer function 200 associates thevarious speed ranges triggered by the capacitive sensors and the speedrate increases controlled by the force sensors. For example, a slowinitial speed range, shown generally at 202, may be ramped at a ratethat accounts for a user's ability to apply a desired varying force onthe control pad to reach a chair set speed limit 204. The speed point202 may be the set point for the center pad 36, for example. This wouldgive the user slow initial speed and provide a wide range of speedcontrol based on force input. Alternatively, the set point may be a fastspeed range setting 206 and require little force input should a user nothave sufficient muscular control.

The principle and mode of operation of this invention have beenexplained and illustrated in its preferred embodiment. However, it mustbe understood that this invention may be practiced otherwise than asspecifically explained and illustrated without departing from its spiritor scope.

What is claimed is:
 1. A powered wheelchair drive control systemcomprising: a head array having a left pad, a right pad, and a centerpad, each pad having a force sensor proportionally responsive to anapplied force from a user's head against each respective pad and acapacitive sensor responsive to the proximity of a user's head relativeto each respective pad, wherein the capacitive sensor provides an activestate signal in response to the presence of the user's head and an offstate signal in the absence of the user's head; and a controllerconfigured to operate at least one wheelchair drive motor in response tosignals generated by the force sensor and capacitive sensor activated bya user's head, the controller programmed with instructions to operatethe at least one wheelchair drive motor at a predetermined speed levelin response to the active state signal of the capacitive sensor in thecenter pad to activate the predetermined speed level in one of a forwardor a reverse direction and to activate the force sensor in response tothe active state of the capacitive sensor to generate a proportionalspeed signal in the one of the forward or reverse directions, thecontroller further configured to control the proportional speed signalof the force sensor through a transfer function.
 2. The poweredwheelchair drive control system of claim 1 wherein the controller isprogrammable to modify the transfer function to adjust an accelerationlevel commanded by the applied force onto the center pad force sensor.3. The powered wheelchair drive control system of claim 1 wherein theproportional speed signal of the center pad force sensor in the one ofthe forward or reverse directions advances the forward or reverse speedabove the predetermined speed level.
 4. The powered wheelchair drivecontrol system of claim 1 wherein the right pad capacitive sensorgenerates a right turn command signal that activates a right turnpredetermined turn rate and the right pad force sensor increases a rightturn speed.
 5. The powered wheelchair drive control system of claim 1wherein the left pad capacitive sensor generates a left turn commandsignal that activates a left turn predetermined turn rate and the leftpad force sensor increases a left turn speed.
 6. The powered wheelchairdrive control system of claim 1 wherein the right pad capacitive sensoractivates the right pad force sensor and the controller is programmed tovary the right wheelchair drive motor speed proportionally to the rightpad force sensor and the left pad capacitive sensor activates the leftpad force sensor and the controller is programmed to vary the leftwheelchair drive motor speed proportionally to the left pad forcesensor.